As means for supplying fuel to an internal combustion engine, a fuel injection device (EFI) is employed, which comprises an injector (electromagnetic fuel injection valve), a fuel pump to feed fuel to the injector, an electronic type controller (ECU) for generating an injection command signal at a predetermined fuel injection timing and an injector driving circuit to feed a driving current to the injector when the injection command signal is given.
When, for example, the fuel is injected into the inside of an intake pipe of the combustion engine by using this fuel injection device, in order to effectively feed the injected fuel into the inside of a cylinder, it is desirable to inject the fuel in the vicinity of an intake stroke of the engine. In order to inject the fuel in the vicinity of the intake stroke, it is necessary to detect the intake stroke. However, in the case of the four cycle internal combustion engine, since one combustion cycle is performed during two rotations of a crank shaft, it is not possible to determine the intake stroke just by detecting a rotational angle of the crank shaft.
For this reason, hitherto in the past, a cam shaft which makes one rotation per one combustion cycle has been attached with a cam shaft sensor which generates a reference signal having a pulse waveform only once for one combustion cycle and, at the same time, attached with a crank shaft sensor for generating a pulse for positional detection every time the crank shaft makes a unit angle rotation, thereby specifying the pulse for each positional detection generated by the crank shaft sensor based on the reference signal generated by the cam shaft sensor, so that it was determined in which stroke the combustion engine was in the rotational angle position of the crank shaft to be detected by each pulse for positional detection.
However, when this method was adopted, it was necessary to attach a sensor to generate a pulse signal for both of the crank shaft and the cam shaft and, therefore, there arose a problem of the cost thereof becoming expensive.
Hence, as shown in Japanese Patent Application Laid-Open Publication No. 10-227252 (227252/1998), there has been proposed a method, wherein a crank shaft sensor for generating a rotational angle detection pulse every time when the crank shaft makes a predetermined angle rotation is attached to the crank shaft and a pressure sensor for detecting the intake air pressure corresponding to a specified cylinder is provided, and the intake air pressure (pressure inside the intake pipe, which is usually negative pressure) detected when the rotational angle detection pulse was generated at a reference rotational angle position on which the crank shaft sensor was set at a specified rotational angle position is compared with the intake air pressure detected at the same position as one rotation before, so that the determination of the stroke of the four cycle internal combustion engine is performed.
According to the method previously proposed as described above, since there is no need to attach the cam shaft sensor, it is possible to perform the stroke determination without an increase in the cost.
Nevertheless, when a throttle valve is sufficiently opened and the combustion engine is operated in a state of a large volume of air always flowing into the inside of the intake pipe, an intake air pressure minutely pulsates due to a large volume of air flow and, therefore, there occurred a problem that it is not possible to adequately perform the determination of the stroke since the difference between the intake air pressure detected at a generating position of the rotational angle detection pulse of this time and the intake air pressure detected at the same position as the last time cannot be accurately distinguished or a magnitude relationship of the intake air pressure is reversed.